ChickenLover

Why do V style engines only have one pcv valve. Why wouldn't the other crankcase use one too? I am currently running two, but only because it helps keep oil from spitting out of my valve breathers. I do not have the crankcases ventilating back into the plenum anymore. IMO crankcase vapors and oil have no business being rerouted into an intake (especially a ported and polished one). I am running some cheapo breathers instead. Why wouldn't it come from the factory with two pcv valves to help keep oil out of the intake and plenum? What am I missing?

amorphous

heh, interesting thread....and I DON'T know the answer.

Riddle me this, why did my friend's '97 TJ 4cyl have NO PCV valve? It LOOKS like one, but is only a "crankcase vent" as Heep calls it.

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Dublin

It's a closed crankcase system, it only requires one pvc valve since both sides are connected by passsageways. Air is brought into one side through the throttle body or intake, into the valve cover, down through the oil drain passage ways, into and through the crank case area, back up through the opposite passages, through the pvc valve, and then back into the manifold for combustable gases to be burned. Say that in one breath. And the cycle repeats. Older systems were not closed and the unburned gases were blown back out the breather or breathers. Not enviromentaly cooperative.

Bumpin' Yota

There is one thing to think about pertaining to the PCV systems and their disfunction in diesels....

Typically there is oxygen/fuel rich air that is blowby around the rings in both diesels and gas engines. The pourpose of the PCV system (as I understand it) is to place a small vacuum in the crank case to evacuate these potentially explosive gasses.

When there is no vaccum you can get what is called "Crankcase Explosion." This occurs when the Air/Fuel mixture in the crank case ignites. Typically there is no damage done other than to blow oil out of oil pan seal. However it is VERY audible. On a smaller engine it will sound like a BIG rock just hit the windshield. On bigger diesel engines it can sound like a cannon firing....

More reason to keep your crank case evacuated....

Id suggest reinstalling the PCV valve and place an oil catch btwn it and the intake plenum.

jimbo74

also, its illegal not to have one properly setup and will cuase you to fail emissions test, possibly with increased emissions or at least the visual portion

ChickenLover

I have been a little worried about those vapors filling the engine compartment. How likely is this 'crankcase explosion' anyway? I've seen a lot of engines that run just simple valve breathers and I have never heard of this danger until now.

rimpainter.com

I have ran PCV breathers on most of my vehicles. I tried it out on my 4Runner, but the "raw" exhaust gasses really stunk. They stunk so bad that they would get sucked in through the fresh air vent and pollute the cabin. Bottom line is that I saw no noticeable performance gain, and it was probably taking some years off my life span. I put mine back on.

Good original question though (it was already answered).

ChickenLover

I've noticed the stink you speak of. But I am pretty adamant on keeping oil out of my ported and polished intake and plenum. It's kind of a pita to take it all apart and clean it out twice a year. Maybe the catch can is a good idea. Or maybe I'll just move the breathers to someplace where I won't smell 'em.

rimpainter.com

I vote catch can. There was a good thread on this going a couple weeks ago. Not sure if I can find it though...

Babypig

On the bottom of the pcv valvethere is a number. What does that number mean. On my old 90 engine it took a pcv valve that had a number 58 on the bottom. Since I've put a 95 engine the part number is different for the pcv valve and it has a 52 on the bottom. Wondering if this has a different opening pressure or closing pressure or the spring is different inside. Could this have caused the high reading I got on my emissions test? The mechanic put the one from the 90 in instead of the new one I had given him.

Flamedx4

[[Why wouldn't the other crankcase use one too?]]

The engine only has one crankcase. Only one vent needed.

mike_d

there may be two heads in a V engine, but there's only one crank case. so you only need on thing to vent it.

ChickenLover

What do you guys think about this:

Routing my breathers to the bottom of my air box. So the vapors will be sucked back into the intake and they'll have to go through the air filter first. This will help keep my port and polish clean and it will rid the engine compartment of all those fumes. And it won't give any oil the chance to be sucked into the intake. Sounds pretty good to me. Am I overlooking anything?

rimpainter.com

Sounds like an interesting idea. My only thought is that hot gasses come out of the breather, so they will be going back into the intake. Most enthusiasts are trying to do two things by installing a breather (eliminate hot air in the intake, and oil residue from forming in the TB). So you will be eliminating one of those variables.

Hmmm...

Babypig

your better off using a pcv gas catch can. There is a thread here on Yotatech. Look under catch can and it should be there. I'm in the process of doing one now.

gwhayduke

Just the fact that the vapors will oil your air filter, which will make it more difficult to suck air through. Probably best to just leave it plumbed as it was from the factory. The crankcase explosion explanation makes sense. Just clean your TB and manifold routinely.